<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>发布订阅模式</title>
</head>
<body>
    <script>
        // 事件触发器
        class EventEmitter {
            constructor() {
                // { 'clcik': [fn1, fn2], 'change': [fn] }
                this.subs = Object.create(null) // 创建原型为null的对象
            }
            // 注册事件
            $on(eventType, handler) {
                this.subs[eventType] = this.subs[eventType] || []
                this.subs[eventType].push(handler)
            }
            // 触发事件
            $emit(eventType) {
                if(this.subs[eventType]) {
                    this.subs[eventType].forEach(handler => {
                        handler()
                    })
                }
            }
        }
        // 测试
        const em = new EventEmitter()
        em.$on('click', () => {
        console.log('click1')
        })
        em.$on('click', () => {
        console.log('click2')
        })

        em.$emit('click')
    </script>
</body>
</html>